Two recent breakthrough studies give the best explanation yet of how exercise helps to prevent heart attacks. Competitive older endurance athletes may have more plaques in their arteries than non-exercisers, but they have the type of plaques that are far less likely to break off and cause heart attacks (Circulation, April 27, 2017;136:138-148; May 2, 2017;136:126-137).

The studies showed that competitive master athletes have:
• low 10-year-history risk scores for likelihood to suffer heart attacks (Framingham study data)
• higher plaque thickness
• more calcium in their plaques
• more stable plaques that are far less likely to break off to cause heart attacks. By comparison, more than 61.5 percent of the older men who did not exercise regularly had "mixed morphology" plaques with much higher risk for breaking off to cause heart attacks.

An editorial accompanying these studies states that having more stable plaques can explain why endurance athletes have such a low rate of heart attacks, and increasing endurance training also increases protection from heart attacks. Michael Joyner of the Mayo Clinic said that the papers show that "Stable plaques plus larger coronary arteries that dilate more in high volume exercisers should be highly protective against coronary events."

How Plaques Form in Arteries
If you understand what happens during a heart attack and what causes these events, you will be able to see why plaque stability is so important. Your immunity is good for you because it helps to protect you from infections. When a germ gets into your body, your immunity makes cells and proteins that attack and kill germs. When the germs are gone, your immunity is supposed to dampen down. However, if your immunity stays active all the time, it can use the same cells and chemicals to attack you to increase your risk for a heart attack.

Different types of bacteria that live in your colon turn your immunity on and off. What you eat determines which types of bacteria grow in your colon because these bacteria eat the same food that you do. These colon bacteria determine how quickly you form plaques in your arteries. Foods favored by the bacteria that turn on your immunity are classified as pro-inflammatory and increase risk for forming plaques in your arteries to increase risk for heart attacks. Anti-inflammatory foods are favored by types of bacteria that help to prevent plaques from forming and decrease heart attack risk. A diet that is high in whole grains, fruits and vegetables, and legumes and nuts is associated with reduced risk for cardiovascular disease, while less healthful diets that are high in sweets, refined grains, juices, red meats and processed meats are associated with increased risk (Journal of the American College of Cardiology, Volume 70, Issue 4, July 2017).

When your immunity stays on all the time to cause inflammation:
• Immune cells and proteins can punch holes in your arteries in the same way that they punch holes in the membranes of invading bacteria.
• The holes bleed and clot.
• Plaques form at the site of the clots and start to cover the inner linings of arteries. We know that cholesterol isn't the primary cause of forming plaques because cholesterol does not start to show up in plaques until long after the holes, bleeding and clotting have occurred on the inner linings of arteries.

Breaking Off of Plaques Causes Heart Attacks
A heart attack is a sudden complete obstruction of the blood flowing to part of the heart muscle. A 90 percent blockage of an artery does not cause a heart attack because blood can still flow through and the heart muscle can still get some oxygen. A heart attack is not caused by plaque buildup on the inner lining of arteries; it is caused by a sudden breaking off of a plaque, followed by bleeding where the plaque broke off. Then clots form at the bleeding sites. Next, the clot extends to block completely the flow of blood to the part of the heart muscle supplied by that artery. The part of the heart muscle deprived completely of blood flow then dies.

How Doctors Measure Plaque Stability
A CT scan can show how stable plaques are (American Journal of Roentgenology, March 2015;204(3):W249-W260). X rays can show the difference between stable plaques that are safe and those that are unstable and more likely to break off to cause heart attacks. Signs of plaque stability include extensive calcification, less lipid-rich areas, increased fibrous areas and structural changes.

Amount of Exercise Does Not Determine Amount of Plaques
A new study shows that older men (average age 60), who had run marathons for 26 to 34 years and completed 27 to 171 marathons, had plaques in their arteries that were related to their own risk factors for heart attacks and not to the number of miles or marathons they had run (Med & Sci in Sports & Ex, July 17, 2017). This suggests that plaques in arteries are not caused by endurance training, but are caused by other factors such as a pro-inflammatory diet, high blood pressure, high cholesterol and previous use of tobacco.

My Recommendations
• To help prevent or reduce plaque formation, follow a heart-attack-preventing diet that is high in anti-inflammatory foods and low in pro-inflammatory foods. This means that you should eat plenty of plants and restrict red meat, processed meats, sugar-added foods, all sugared drinks and fried foods.
• Avoid overweight
• Do not smoke
• Limit or avoid alcohol
• To stabilize existing plaques and widen your coronary arteries, try to exercise every day for at least a half hour a day. Exercising more than that may be even more protective.

Caution:Intense exercise can cause a heart attack in people with blocked arteries. Check with your doctor before starting a new exercise program or increasing the intensity of your existing program.

About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities.
Read More